Ocean/atmosphere variability related to the development of tropical Pacific sea-surface temperature anomalies in the CCSM2.0 and CCSM3.0

Bruce T. Anderson, Boston University (brucea@bu.edu)

Eric Maloney, Oregon State University

Introduction

Researchers have spent considerable time investigating forcing mechanisms for the El Niño/Southern Oscillation (ENSO) as well as the evolution of the atmospheric and oceanic components of the ENSO systemOne intriguing set of results involves fields in the extra-tropics that may be related to the initiation of ENSO eventsIn this talk, we will attempt to build upon this research by:

Identifying extra-tropical ocean/atmosphere anomaly patterns that represent statistically significant precursors to the onset of ENSO eventsComparing those patterns found in the simulated system with previously-identified patterns in the observed systemInvestigating the simulated and observed evolution of the ENSO system as it relates to these patterns

Data Sets

NCEP ReanalysisAtmospheric data at 2.5-degree resolutionSea-surface temperature data at T62 resolution (approximately 2 degrees in latitude and longitude)~53 years of data (1948-2000)

Community Climate System Model (CCSM2.0)Monthly data at T42 resolution (approximately 2.8 degrees in latitude and longitude)250 years of data

Community Climate System Model (CCSM3.0)Monthly data at T85 resolution (approximately 1.4 degrees in latitude and longitude)500 years of data

Statistical Techniques

Canonical Correlation AnalysisMultivariate regression algorithm designed to maximize the correlation between the time-series from different datasets, P(x,t) and T(y,t)Produces a set of canonical factor (CF) time-series that isolate the highest correlated modes of variability within the two datasetsBased upon solving the eigenvalue equation:

UU−1

TU′TT

−1TU −λ

⎛

⎝

⎜ ⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟ ⎟

A=0

λ - Eigenvalues: Represents correlation between canonical factor time-seriesA - Eigenvectors: Represents "spatial maps" for canonical factors of T

Jan.-Mar. SLP and SSTs the Following Year

Time-Series

Sea-Level Pressure

Sea-Surface Temp.

ENSO in Observations and Climate Simulations

(Deser et al., 2005 - Draft)

Comparison of Simulated and Observed Patterns

Observed: CF3

Simulated: CF1

yr+1

yr+1

Comparison of Simulated and Observed Patterns

Observed: CF1

Simulated: CF2

yr+1

yr+1

Comparison of CCSM2 and CCSM3 Patterns

CCSM2: CF1

yr+1

CCSM3: CF1

yr+1

Comparison of CCSM2 and CCSM3 Patterns

CCSM2: CF2

yr+1

CCSM3: CF2

yr+1

Simulated and Observed Temporal Patterns

Evolution of Simulated SSTs for CF1

Evolution of Simulated SSTs for CF1

Evolution of Simulated SSTs for CF2

Evolution of Simulated SSTs for CF2

Evolution of Mixed Layer Depth and SSTs

Year+1Year-1 Year 0

CCSM2

CCSM3

Evolution of Mixed Layer Depth and SSTs Con’t

Year+1Year-1 Year 0

CCSM2

CCSM3

Evolution of Mixed Layer Depth and SSTs con’t.

(Meinen and McPhaden, 2001)

Sea Surf. Temp.

Mixed Layer Depth

Model

Obs. 1993-99

Conclusions

Equatorial Pacific SST anomalies appear to be partly related to large-scale atmospheric modes of variability 12-15 months prior to the maturation of the JFM ENSO

One mode is related to the strong biennial oscillation in which La Niña-related SLPs precede El Niño-like SSTs the following winterThe second mode of variability indicates that boreal-winter tropical Pacific SSTs are also initiated by SLP anomalies over the subtropical central and eastern north Pacific

The evolution of both modes is characterized by recharge/discharge within the equatorial subsurface temperature field

For the first mode, the basin-average equatorial Pacific isotherm depth anomalies, isotherm-slopes, and SSTs show significant oscillatory behavior up to two years prior to ENSO eventsFor the second canonical factor, the recharge/discharge mechanism is induced concurrent with the JFM SLP pattern itself.

? Role of “pre-conditioning” of basin-scale heat content andthermocline slope

? Low-frequency modulation of subtropical influence

Non-Stationarity in the Simulated and Obs. Modes

Recharge/Discharge Paradigm for ENSO

(Meinen and McPhaden, 2000)

El Nino/Southern Oscillation

El Nino/Southern Oscillation Impacts

El Nino/Southern Oscillation Impacts

CCSM2 and CCSM3 Temporal Patterns